Guide: How to clean a dirty fuel tank, filter, pump, and injector

Poor fuel quality in some areas of the world can cause a motorcycle to not run properly. There were five occasions in Africa where I needed to clean my fuel tank, fuel filter, and fuel pump. I've started to understand what causes these issue and how to remedy it. This guide is based on my personal experiences and reading online. This is a learning curve for me!

Symptoms of dirty fuel system

Reduced top speed.
Starting the motorcycle requires more time.
When accelerating the engine would sputter/hesitate/bog causing the front end to dive forward. This is less noticeable in higher gears.
When the problem is extremely bad, my motorcycle would run for a few seconds and then cut out (read my blog post here).

Causes

Here's a brief analysis of what I suspect caused issues for me on my Honda CRF250L. Please understand there's quite a bit of guess work here.

Benin (read my blog post here)—I entered Africa from Morocco and had a Twin Air fuel tank filter (read my Twin Air fuel tank filter review here). Prior to Benin, I had not used any fuel system cleaner. I suspect the cause was an accumulation of dirt since the start of the journey and the one occasion I refueled with black market fuel from a glass container stored in direct sunlight in Benin.
Angola (read my blog post here)—I refueled in Luanda immediately after a fuel tanker resupplied a fuel station during a fuel crisis. I suspect the cause was that the fuel station did not allow time for any sediment (e.g., dirt, rust) in their underground storage to settle before selling the fuel.
Namibia—I cleaned the fuel filter and fuel pump. It was part of a service, and I don't think there were any symptoms that prompted me to clean the filter and pump.
Malawi—I cleaned the inside of the fuel tank, fuel filter, and fuel pump, because I experienced minor bogging/hesitation under acceleration.
Tanzania—The motorcycle had a loss of power that was noticeable at high speed and during acceleration. I suspect the cause was leaving the motorcycle unused in partial shade from sunlight (depending on time of day) for 3.5 weeks whilst at a cool beach resort (read my blog post here). Starting the motorcycle was difficult, which I suspect was caused by the evaporation of high-volatility compounds required as vapour for combustion (read more about fuel volatility here) or the fuel gumming up and blocking passages (read ADVrider thread here).

I have electronic fuel injection (EFI) on my Honda CRF250L motorcycle. I read somewhere that the injector has smaller diameter holes for fuel to pass through than that of a carburettor. Sounds logical but I don't have knowledge or evidence for this.

Advice before you start

Only start cleaning when you're close to help (i.e., walking distance) in case something goes wrong.
Clean your motorcycle, if possible. Especially around the fuel tank area.
Read the entire article from start to finish, so you're away of what's required before dismantling parts of the fuel system. I've done this in the bush in Angola (read my blog post here), which was a necessity and definitely not a choice—thankfully, I had everything required!

Cleaning inside a fuel tank

The aim of the first stage is to remove the fuel tank and fuel from the tank. How to do this depends on your motorcycle. For example, with my CRF250L and Acerbis tank, I remove the fuel tank first and then drain it. Also, the fuel pump assembly (part # 16700-KZZ-D21) is removed from inside the fuel tank.

Once the fuel tank has been removed, inspect it to assess the dirt, so you can review the effectiveness of cleaning as you go. On my Acerbis fuel tank, I've observed the following:

lines of dirt from where the fuel level has not changed whilst parked,
small particles of dirt sitting at the bottom near the fuel pump, and
a thin layer of dirt all over the inside including above the fuel level.

Here are some photos of what it looks like inside the fuel tank. It's difficult to see in the photos, but obvious when seen in real life.

Method: Scrubbing with carburettor cleaner

My first approach to clean the fuel tank was to spray carburettor cleaner inside the tank. This dislodges and eats some dirt by itself. Some carburettor cleaners work better than others, so read my carburettor cleaner review here.

Also scrubbing improves the effectiveness. This is where improvisation is required. A toothbrush strapped to a tyre lever with zip ties was capable of cleaning inside the fuel tank. Duct tape is not advisable because the chemicals in the cleaner can degrade the glue on the duct tape.

Toothbrush gaffer taped to tyre lever for cleaning inside of fuel tank. Parakou, Benin.

I've also used kitchen cleaning brushes that have a wire handle with plastic bristles. The wire handles tend to bend easily.

Reaching the furthest parts of the inside can be a challenge. Having a natural colour fuel tank that allows light through makes it easy to see what you're doing.

Method: Bleach

Scrubbing with carburettor cleaner can be a challenge because of the cleaner's quality and reaching every area inside the tank with a brush.

The vendor of my Acerbis fuel tank says the fuel tank is made of reticulated polyethylene. If you read a polyethylene chemical resistance chart, you'll notice chemicals that are present in household products. Sodium hypochlorite is in chlorine bleach and the chart states polyethylene is resistant to it. So, I searched for bleach listing this ingredient in a shop in Tanzania and found it!

I used diluted bleach in a small area of the fuel tank and let it rest whilst periodically checking it. After about 15-30 minutes, the plastic looked cleaner and the bleach solution contained dirt particles. I could not see any degradation to the fuel tank.

Once I was happy that it was safe, I added more diluted bleach and let it rest for about 12 hours whilst periodically swilling the solution to cover the entire inner surface area of the fuel tank.

Bleach was more effective than scrubbing with carburettor cleaner inside the fuel tank, because bleach cleans the areas that could not be reached with a brush. The end result was very good!

Cleaning a fuel filter

On my Honda CRF250L, the fuel filter sits inside the fuel pump assembly inside the fuel tank. The first time I removed the fuel filter, it was covered in black, fine sludge. This is easily seen on the toilet paper below.

Dirty fuel filter from Honda CRF250L. Parakou, Benin.

To clean this type of fuel filter, I sprayed carburettor cleaner on the fuel filter. Squeezing the fuel filter with my hands produced a black liquid that dripped out. Careful—it can be very dirty. Repeatedly spraying and squeezing with my hands eventually produced a clearer liquid carrying less dirt out of the fuel filter.

Cleaning a fuel pump

Cleaning the fuel pump is best done with carburettor cleaning and scrubbing with a toothbrush. I didn't try bleach because I don't know what is inside the fuel pump.

The fuel pump assembly can harbour dirt particles and the white plastic casing can be stained yellow-brown. Soaking only the white plastic—not O rings and fuel pump—in diluted bleach works well at removing the stained dirt. Spraying with carburettor cleaner and scrubbing with a toothbrush also works, but reaching every area is a challenge.

Cleaning a fuel injector

The fuel injector can be a challenge to clean without an ultrasonic cleaner. Instead, it's possible to use carburettor cleaner. I have only attempted this once.

Initially, I left the nozzle of the injector sitting in a cap of carburettor cleaner. I didn't know how to asses whether there was a problem and whether this was fixing the problem.

Fuel injector from Honda CRF250L sitting in small amount of cleaner. Parakou, Benin.

Another approach is to secure a section of pipe to the injector where the fuel enters. Somehow fix the other end of the pipe to the can of carburettor cleaner. Improvisation is required here. The idea is that spraying the can of carburettor cleaner will create some pressure to feed the cleaner through the pipe into the injector. It is certainly not perfect and my improvisation leaked.

Remove the motorcycle's battery and connect the terminals to the injector. I used an electrical tester screw driver that had a wire and crocodile clip. I can't remember what I used for the second wire. Again, improvisation is required here with whatever you have to hand.

Now, power the injector and at the same time spray the carburettor can. This is far from a perfectly working method, but I managed to see carburettor cleaner being sprayed out of the injector in a uniform pattern. I confirmed that every hole was not blocked.

Reassembly

It's important to remember where the electrical cables are connected in the fuel pump assembly before unplugging them. Here are photos of the orders for the fuel pump assembly in the Honda CRF250L.

If the CRF250L dash flashes an error code, it's likely the wiring in the fuel pump assembly is incorrect.

When turning the ignition key, you should hear the pump prime itself. My CRF250L makes a buzz sound when it does this.

It's wise to use new, clean fuel when starting the motorcycle.

Sometimes, I've used fuel system cleaner for the first tank of fuel. The idea is to give a final cleanse of the fuel system.

Recommendations for prevention

Here are some tips for preventing a dirty fuel system.

Use a fuel filter when refueling!
Source quality fuel, and avoid the black market, if possible.
Protect storage from sunlight. This includes the fuel tank and auxiliary fuel storage.
Use fuel system cleaner (purchased in fuel stations). After a recommendation from KTM in Lomé, Togo, this is now part of my regular maintenance in Africa.